A conventional passenger protection system for a vehicle disclosed in JP2007-500650A includes a seat apparatus having a motor and a control unit controlling operation of the motor. The motor drives a seat to move so that a position of the seat is adjusted. When a position of the seat is normally adjusted in the seat apparatus, the seat is moved at a first speed. In urgent cases where a vehicle may collide with an obstacle, the seat is moved at a second speed, which is higher than the first speed so that a position of the seat is quickly adjusted in order to protect a passenger of the vehicle from an impact due to the collision. In this way, when a position of the seat is normally adjusted in consideration for comfort and easiness of the seat position adjustment for the passenger, the motor is controlled so that the seat is actuated at a relatively low speed.
According to the conventional passenger protection system, when the seat driven by the motor starts moving, the motor may require a large driving force due to an effect of friction between gears arranged in a seat actuating mechanism and an effect of hardening of grease applied to the gears. On the other hand, when the seat is normally moved in order to change a position of the seat, the motor is controlled so that the seat is moved at a low speed. Accordingly, the seat is not moved and an operating speed of the seat is extremely reduced because of an insufficient driving force of the motor.
A need thus exists for a seat apparatus, which is not susceptible to the drawback mentioned above.